Image recording member

ABSTRACT

An image recording member comprises a substrate and a recording layer containing a conductive agent, a leuco base, and a phenol compound.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an image recording member for recording images by application of electrical current and further to a process for recording images.

2. Description of the Prior Art

Recording of electrical signals as images has been increasing from year to year with the development of facsimile, printers and recorders. Heretofore, electrical discharge recording and electrolyte recording systems have been mainly used for such purpose, but these conventional systems suffer from the generation of bad odor and dust upon recording, limited handling due to the wet system and low recording image quality.

Japanese Pat. Publication No. 22341/1963, Japanese Patent Application Laid-open Nos. 101935/1973 and 122746/1974, and Japanese Patent Publication No. 46953/1974 disclose electric conduction recording systems producing images by applying electric current to a recording member having a recording layer containing a metal compound capable of forming color by electric reduction dispersed in a matrix or a recording member having a recording layer containing a color forming agent capable of coloring by heat and a conductive agent, and these electric conduction recording systems have been practically used. These recording systems are better than electrical discharge recording and electrolyte recording systems because the electric conduction recording systems give less odor and dust and are easy in handling due to their dry nature.

As a color forming agent colored by heat, there has been known a combination of a leuco base and an acidic substance. The color formation is caused by chemical reaction of the leuco base with the acidic substance. In general, a finely divided leuco base and an acidic substance are dispersed in a matrix and a heat image is applied thereto to melt one or both of them and cause contacting therebetween resulting in color formation. This technique has been used in conventional heat-sensitive recording and the image formation is effected by bringing a heat source such as a thermal head and the like into contact with a surface of a heat-sensitive recording paper having a recording layer containing a leuco base and an acidic substance dispersed in a matrix. Further, Japanese Pat. application Laid-open Nos. 101935/1973 and 122746/1974 and Japanese Pat. Publication No. 46953/1974 disclose an electric conduction recording system utilizing a heat-sensitive color forming agent composed of the above-mentioned leuco base and acidic substance. This process comprises applying electric current through a conductive agent to a recording layer composed of the above mentioned leuco base and acidic substance and further, the conductive agent, dispersed in a matrix, and thereby generating partly heat, which causes color-developing of the color forming agent. A disadvantage of this process is the coexistance of a conductive agent as well as the leuco base and the acidic substance in the recording layer different from a usual heat-sensitive recording. In other words, the coexistance of the color forming agent composed of the leuco base and acidic substance together with a conductive agent results in a remarkable unstable state as compared with a heat-sensitive paper which does not contain any conductive agent. The above mentioned conduction recording member has disadvantages such as low shelf life of the white paper, increased coloring of the background as the time lapses, and low recording density of the white recording paper with the lapse of time. These changes with the lapse of time are remarkably accelerated by light, heat and humidity. On the other hand, the recorded image is also subjected to lowering of its image density and changing of color with the lapse of time. The color changing and fading of images are markedly accelerated by human excretion as well as light, heat and humidity. Such tendency is also observed in the case of heat-sensitive recording papers which do not contain any conductive agent to some extent, but such remarkable changes are caused by the presence of the conductive agent affecting the color forming agent. Though the detailed mechanism which increases fog and accelerates color changing and fading is not clear, it seems sure that the conductive agent affects them to a great extent since a system containing no conductive agent is not subjected to such problem so much.

As usual conductive agents, there are metal compounds such as zinc oxide, copper iodide, tin oxide and the like, metal powder, compounds containing zeolitic water such as zeolite mineral, organic high polymer electrolytes and inorganic electrolytes. The above mentioned problem is caused more or less even if any conductive agent is used.

Among these conductive agents, metal compounds, metal powders, and zeolitic minerals used as pigment have some active points on the surface of the particles and the catalytic effect of the active points accelerates chemical reactions such as oxidation, reduction, decomposition and the like, of the leuco base, acidic substance and dye after being colored. As the result, it is considered that lowering of color forming density and formation of fog are caused by substantial decrease of the coloring agent or formation of unnecessary color forming agents. Further, when electrolytes are used as a conductive agent, the mechanism is different somewhat, but as the result of ion exchange and salt forming bonding of leuco base, acidic substance or dye after coloring, there seems to be caused color changing and fading. This mechanism is only an estimation, but anyway when a conductive agent is present, color changing and fading occur disadvantageously.

SUMMARY OF THE INVENTION

An object of this invention is to provide an improved image recording member free from color changing and fading, particularly used for conduction recording.

Another object of this invention is to provide an image recording member of excellent storage stability.

A further object of this invention is to provide an image recording member capable of corresponding to a fine change of electric conduction and giving excellent recording image quality and excellent reproducibility of image tone.

Still another object of this invention is to provide an image recording member of easy handling.

A still further object of this invention is to provide a process for conduction recording producing excellent images.

According to the present invention, there is provided an image recording member which comprises a substrate and a recording layer overlying the substrate and containing a conductive agent, a binder, a leuco base, and at least one phenol compound selected from the class of

(I) phenolic resin having a softening point of from 40° to 200° C. obtained by reacting a phenol compound having, in one molecule, at least one phenolic hydroxy group, and at least two unsubstituted positions at the ortho and/or para positions as to the phenolic hydroxy group, with at least one bonding agent selected from the class of lower aliphatic aldehydes and derivatives thereof, lower alkyl vinyl ethers, bifunctional condensing agents, and a cross linking agent containing sulfur,

(II) phenol compound containing, in one molecule, one or more of --S--, --S--S--, --SO₂ --, and --SO-- bonding portion and being solid at normal temperature and capable of being liquified or vaporized at a temperature higher than 50° C. and

(III) phenol compound having, in one molecule, one or two phenolic hydroxy groups and at least one alkyl moiety containing 4-30 carbon atoms and melting point of from 40° to 200° C.

According to another aspect of the present invention, there is provided a process for conduction recording which comprises bringing a stylus into contact with a recording layer containing a conductive agent, a leuco base, a phenol compound and a binder and provided on a substrate having a conductive layer, setting a return electrode on the conductive layer and applying electric current to the recording layer through the stylus to form images, or bringing a stylus into contact with said recording layer provided on a substrate, setting a return electrode on the recording layer and applying electric current to the recording layer through the stylus to form images.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1, FIG. 2 and FIG. 3 schematically illustrate the structure of an image recording member of the present invention and a recording method.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will be described by referring to the drawing.

Referring to FIG. 1, a recording layer 1 is provided on a conductive layer 2 overlying a substrate 3. The recording layer 1 contains at least a conductive agent, leuco base, phenol compound and binder (a color developing accelerating agent may be added thereto). The image recording member in FIG. 2 is a modification of that in FIG. 1 and the recording layer is composed of a conduction layer 5 containing mainly a conductive agent and an image forming layer 6 containing mainly a color forming agent. FIG. 3 is a further embodiment of an image recording member having a substrate 3 and a recording layer 1 overlying the substrate. In the drawing, reference numerals 4, 7 and 8 denote a power source, a recording needle (stylus) and a return electrode. The return electrode is set on conductive layer 2 or recording layer 1. The polarity given to the stylus may be positive or negative and AC.

In the following, various components constituting each recording layer are described.

(I) Conductive agent

The conductive agent used in the present invention imparts conductivity to the matrix. The conductive agent may be metals, metallic vapor-deposited members, metal oxides, metal sulfides, metal phosphides, metal halides, alloys, carbon compounds, clay minerals, zeolitic minerals, which may be in a form of powder, and conductive polymers.

Representative conductive agents are powders of metal such as silver, gold, aluminum, nickel, cobalt, tin, bismuth, cadmium, indium and the like, powders composed of the above-mentioned metals vapor-deposited on a carrier such as alumina and silica, metal oxides such as titanium oxide, zinc oxide, lead oxide, tin oxide, calcium oxide, nickel oxide, indium oxide, tinindium oxide, molybdenum oxide, tungsten oxide and the like, metal sulfides such as zinc sulfide, calcium sulfide, copper sulfide, Cd₄ GeS₆, Cd₄ SiS₆, Zn₄ GeS₆, Zn₄ SiS₆ and the like, metal phosphides such as aluminum phosphide, gallium phosphide, gallium aluminum phosphide and the like, metal halides such as copper chloride, silver chloride, silver bromide, silver iodide, thallium chloride, thallium iodide, lead chloride, cuprous iodide and the like, alloys such as zinc-selenium, zinc-tellurium-selenium, magnesium-tellurium and the like, carbon compounds such as silicon carbide, carbon fluoride and the like, clay minerals such as montmorillonite, kaolinite and the like, zeolites such as faujasite, mordenite synthetic zeolite and the like, and conductive polymers such as poly-4-vinylbenzyltrimethylammonium chloride, sodium polymethacrylate and the like.

Zeolites, natural or synthetic, used in the present invention may be classified as follows:

    ______________________________________                                         (1) Analcime                                                                     Group:                                                                       Analcite    NaAlSi.sub.2 O.sub.6 . H.sub.2 O                                   Pollucite   (Cs,Na)AlSi.sub.2 O.sub.6 . xH.sub.2 O   (x<10)                    Viseite     Ca.sub.10 Na.sub.2 Al.sub.10 Si.sub.6 P.sub.10 (H.sub.3).sub.1                 2 (H.sub.2 O).sub.16 . O.sub.96                                    Kehoesite   Zn.sub.5.5 Ca.sub.2.5 Al.sub.16 P.sub.16 (H.sub.3).sub.16                      (H.sub.2 O).sub.32 O.sub.96                                        (2) Sodalite                                                                     Group:                                                                       Hydrosodalite                                                                              Na.sub.8 (Al.sub.6 Si.sub.6 O.sub.12)(OH).sub.2                    Faujasite   Na.sub.28.6 Ca.sub.14.8 (Al.sub.57.6 Si.sub.134.4 O.sub.384)26                 2 . 3H.sub.2 O                                                     Molecular Sieve *A                                                                         Na.sub.12 (Al.sub.12 Si.sub.12 O.sub.24)Na AlO.sub.2 .                         29H.sub.2 O                                                        Molecular Sieve *X                                                                         Na.sub.2 (Al.sub.2 Si.sub.2.8 O.sub.9.6) . xH.sub.2 O                          (x≃6)                                                Molecular Sieve *Y                                                                         Na.sub.2 O . Al.sub.2 O.sub.3 . 3˜6 SiO.sub.2 .                          xH.sub.2 O                                                         Molecular Sieve* SK                                                                        substantially identical to faujasite                                *Synthetic Zeolite manufactured by Union Carbide Co.                          (3) Chabazite                                                                    Group:                                                                       Chabazite   (Ca,Na.sub.2)Al.sub.2 Si.sub.4 O.sub.12 . 6H.sub.2 O               Gmelinite   (Na.sub.2, Ca)Al.sub.2 Si.sub.4 O.sub.12 . 6H.sub.2 O              Erionite    (Ca,Mg . Na.sub.2 . K.sub.2) . Al.sub.2 Si.sub.4 O.sub.12 .                    6H.sub.2 O                                                         Levynite    Ca(Al.sub.2 Si.sub.4 O.sub.12) . 6H.sub.2 O                        Molecular Sieve *R                                                                         the same as Chabazite                                              Molcular Sieve *S                                                                          the same as Gmelinite                                              Molecular Sieve *T                                                                         the same as Elionite                                               (4) Natrolite                                                                    Group:                                                                       Natrolite   Na.sub.2 (Al.sub.2 Si.sub.3 O.sub.10) . 2H.sub.2 O                 Mesolite    Na.sub.2 Ca.sub.2 (Al.sub.6 Si.sub.9 O.sub.30) . 8H.sub.2 O        Scolecite   Ca(Al.sub.2 Si.sub.3 O.sub.10) . 3H.sub.2 O                        Thomsonite  NaCa.sub.2 (Al.sub.5 Si.sub.5 O.sub.20) . 6H.sub.2 O               Edingtonite Ba(Al.sub.2 Si.sub.3 O.sub.10) . 4H.sub.2 O                        Gonnardite  Na.sub.2 Ca(Al.sub.4 Si.sub.6 O.sub.20) . 6H.sub.2 0               Rhodesite   KnaCa.sub.2 (H.sub.2 Si.sub.8 O.sub.20) . 5H.sub.2 O               Mountainite KNa.sub.2 Ca.sub.2 (HSi.sub.8 O.sub.20) . 5H.sub.2 O               (5) Harmotome                                                                    Groups:                                                                      Harmotome   Ba.sub.2 (Al.sub.4 Si.sub.12 O.sub.32) . 4H.sub.2 O                Phillipsite (KxNa.sub.1-x).sub.5 Al.sub.5 Si.sub.11 O.sub.32 . 10H.sub.2                   O                                                                  Gismondite  Ca(Al.sub.2 Si.sub.2 O.sub.8) . 4H.sub.2 O                         Molecular Sieve *B                                                                         Na.sub.2 (Al.sub.2 Si.sub.3 O.sub.10) . 5H.sub.2 O                 Garronite   NaCa.sub.2.5 (Al.sub.3 Si.sub.5 O.sub.16).sub.2 . 13.5H.sub.2                  O                                                                  (6) Mordenite                                                                    Group:                                                                       Mordenite   Na(AlSi.sub.5 O.sub.12) . 3H.sub.2 O                               D'achiardite                                                                               (Na.sub.2 Ca).sub.2 Al.sub.4 Si.sub.20 O.sub.48. 12H.sub.2 O       Ferrierite  Na.sub.1.5 Mg.sub.2 (Al.sub.5.5 Si.sub.30.5 O.sub.72) .                        18H.sub.2 O                                                        Zeolon**    the same as Mordenite                                              **manufactured by Norton Co.                                                   Some zeolites of non-determined structure as shown below.                        Heulardite    Ca(Al.sub.2 Si.sub.7 O.sub.18) . 6H.sub.2 O                    Clinoptilotite                                                                   Na.sub.0.95 K.sub.0.30 Ca.sub.0.5 (Al.sub.1.35 Si.sub.7.05 O.sub.18) .         5H.sub.2 O                                                                   Stilbite                                                                         Ca(Al.sub.2 Si.sub.7 O.sub.18) . 7H.sub.2 O                                  Epistilbite                                                                      Ca(Al.sub.2 Si.sub.6 O.sub.16) . 5H.sub.2 O                                  Brewsterite                                                                      (Sr,Ba,Ca)Al.sub.2 Si.sub.6 O.sub.16 . 5H.sub. 2 0                           Laumontite                                                                       Ca(AlSi.sub.2 O.sub.6) . 4H.sub.2 O                                          Yugawaralite                                                                     Ca(Al.sub.2 Si.sub.5 O.sub.14) . 3H.sub.2 O                                  Paulingite                                                                       (K,Ca,Na).sub.120 [(Al,Si).sub.580 O.sub.1160 ]. 690H.sub.2 O                Aschcroftine                                                                     [KNa(Ca,Mg,Mn)] .sub.120                                                       (Al.sub.160 Si.sub.200 O.sub.720) . 320H.sub.2 O                             Bikitaite                                                                        LiAlSi.sub.2 O.sub.6 . H.sub.2 O                                             ______________________________________                                    

All the above compounds are applicable to the invention. Zeolite-like compounds used in the present invention include the following minerals.

(1) Zeolite-like silicate

They are not classified into Zeolite, but contain zeolitic water.

    ______________________________________                                         Beryl      Al.sub.2 Be.sub.3 [Si.sub.6 O.sub.18 ]. nH.sub.2 O                  Cordierite Mg.sub.2 Al.sub.3 [AlSi.sub.5 O.sub.18 ]. nH.sub.2 O                Milarite   KCa.sub.2 AlBe.sub.2 [Si.sub.12 O.sub.30 ]O.5H.sub.2 O              Osumilite  (K,Na,Ca)(Mg,Fe).sub.2 (Al,Fe).sub.3                                           [ (Si,Al).sub.12 O.sub.30 ] . H.sub.2 O                             Hydrated                                                                       Nepheline  KNa.sub.3 (Al.sub.4 Si.sub.4 O.sub.16) . nH.sub.2 O                 Cancrinite Na.sub.6 Ca.sub.6 (Al.sub.6 Si.sub.6 O.sub.24)CO.sub.3 .                       3H.sub.2 O                                                          Buddingtonite                                                                             NH.sub.4 AlSi.sub.3 O.sub.8 . 0.5H.sub.2 O                          (2) Other zeolite-like compounds                                               I) Germanate                                                                              M.sub.3 [HGe.sub.4 (GeO.sub.4).sub.3 O.sub.4 ] . 4H.sub.2 O: M                 is a metal ion.                                                     II) Phosphate, Arsenate,                                                       Scorodite  FeAsO.sub.4 . 2H.sub.2 O                                            Pharmacosiderite                                                                          K[Fe.sub.2 (OH).sub.4 (AsO.sub.4).sub.3 ] . 6˜7H.sub.2                   O                                                                   III) Water containing metal oxide                                              Psilomelane                                                                               (Ba, H.sub.2 O).sub.2, Mn.sub.5 O.sub.10                            IV) Three structure complex                                                    Prussian blue                                                                             M.sub. 3 [Fe(CN)6].sub.2 . 12H.sub.2 O, (M=Mn,Fe,Co,Ni,Zn,Cd)       Weddellite CaC.sub.2 O.sub.4 . (2 + x)H.sub.2 O,   (x -< 0.5)                  ______________________________________                                    

(II) Leuco base

The leuco base is usually a colorless or lightly colored solid which is colored when brought into contact with an acidic substance used in this invention. The leuco base includes known dye leuco bodies such as triphenylmethane series, fluoran series, phenothiazine series, auramine series, spiropyran series and the like.

(III) Phenol compound

The phenol compound prevents color changing and fading of the colored images or increases storage stability of the recording member, and causes a color forming reaction when brought into contact with the leuco base as mentioned above.

The phenol compounds include the following phenol compounds (1), (2) and (3) in detail.

(1) Phenolic resin having a softening point of from 40° to 200° C. obtained by reacting a phenol compound having, in one molecule, at least one phenolic hydroxy group and at least two unsubstituted positions ortho and/or para to the phenolic hydroxy group, with at least one bonding agent selected from the class of lower aliphatic aldehydes and derivatives thereof, lower alkyl vinyl ethers, bifunctional condensing agents, and a cross linking agent containing sulfur.

(2) Phenol compound containing, in one molecule, one or more of --S--, --S--S--, --SO₂ -- and --SO-- bonding portion and being solid at normal temperature and capable of being liquified or vaporized at a temperature higher than 50° C,

(3) Phenol compound having, in one molecule, one or two phenolic hydroxy groups and at least one alkyl moiety containing 4-30 carbon atoms and a melting point of from 40° to 200° C.

Representative phenol compounds are as shown below.

(a) Phenolic resins obtained by the polycondensation of 4, 4'-isopropylidene diphenol or 4, 4'-sec-butylidene diphenol with formaldehyde or acetaldehyde in an aqueous alcohol in the presence of a hydrochloric acid catalyst, washing the resulting oily product and reprecipitating with water.

(b) Phenolic resins having a softening point of from 40° to 200° C. obtained by reacting a phenol compound having, in one molecule, at least one phenolic hydroxy group and having at least two unsubstituted positions ortho and/or para to the phenolic hydroxy group with at least one bonding agent selected from the class of lower aliphatic aldehydes and derivatives thereof, lower alkyl vinyl ethers, bifunctional condensing agents and cross linking agents containing sulfur. The softening point here is that determined by ring and ball test.

Representative starting materials therefor are, for example, as shown below.

(1) Phenol compounds:

Phenol, m-cresol, 3,5-xylenol, 4,4'-isopropylidenediphenol, 4,4'-sec-butylidenediphenol, 4,4'-ethylidenediphenol, 4,4'-cyclohexylidenediphenol, 4,4'-(1-methylpentylidene)diphenol, 4,4'-(1-ethylbutylidene)diphenol, 4,4'-isopropylidenedicatechol, 4,4'-ethylenediphenol, 4,4'-hexamethylenediphenol, 4,4'-benzylidenediphenol, 4,4',4"-methyne-tris-phenol, 4,4'-bishydroxyphenyl sulfide, 4,4'-bishydroxyphenyl disulfide, 4,4'-bishydroxyphenyl sulfone, 4,4'-dihydroxybenzophenone, 2,2'-isopropylidenediphenol, 2,2'-sec-butylidenediphenol, 2,2'-ethylenediphenol, 2,2'-bishydroxyphenyl sulfide, 2,2'-bishydroxyphenyl disulfide, 2,4' -isopropylidenediphenol, bis-(2,4'-dihydroxyphenyl)sulfide and the like.

(2) Cross linking agent:

Formaldehyde, acetaldehyde, propionaldehyde, butylaldehyde, acrolein, glyoxal, malonaldehyde, methylglyoxal, glycol aldehyde, chloral, paraformaldehyde, trioxane, paraaldehyde, acetals, methyl vinyl ether, ethyl vinyl ether, sulfur, sulfur monochloride, sulfur dichloride, sulfur pentachloride, sulfur dibromide, α,ω -dihalogenated hydrocarbon and the like.

(c) Sulfur containing phenol compounds:

3-methyl-4-hydroxyphenyl ethyl sulfide, 2-hydroxydiphenyl sulfide, 2-hydroxyphenyl-2',4'-dichlorophenyl sulfide, 4-hydroxyphenyl-2'-chlorobenzyl sulfide, 3 -methyl-4-hydroxyphenylbenzyl sulfide, 4,4'-dihydroxythiobenzophenone, ethyl N-(4-hydroxyphenyl) dithiocarbamate, thioacetic acid-S-4-hydroxyphenyl ester, 4,4'-dihydroxydiphenyl sulfide, 2,4'-dihydroxydiphenyl sulfide, 2,2'-dihydroxydiphenyl sulfide, 4,4'-dihydroxydiphenyl disulfide, 4,4'-dihydroxydiphenyl sulfone, 4,4'-dihydroxydiphenyl sulfoxide, 2,2'-dihydroxy-5,5-dichlorodiphenyl sulfide, 2,2'-dichloro-4,4'-dihydroxydiphenyl sulfide, 3,3',5,5'-tetrachloro-2,2'-dihydroxyphenyl sulfide, 2,2'-dihydroxy-5,5'-dimethyldiphenyl sulfide, 2,2'-dimethyl-5,5'-di-tert-butyl-4,4'-dihydroxydiphenyl sulfide, 2,2',4,4'-tetrahydroxydiphenyl sulfide, 2,2',4,4'-tetrahydroxydiphenyl disulfide, 2,2',4,4'-tetrahydroxydiphenyl sulfone, 2,2',4,4'-tetrahydroxydiphenyl sulfoxide, 2,2',4,4'-tetrahydroxy-5,5'-dichlorodiphenyl sulfide, 2,2',4,4'-tetrahydroxy-5,5'-diethyldiphenyl sulfide, 4,4'-di(p-hydroxyphenyl) diphenyl sulfide, 4,4'-di(p-hydroxyphenyl)diphenyl disulfide, 2,2'-dihydroxy-6,6'-dinaphthyl sulfide, 2,2'-dihydroxy-6,6'-dinaphthyl disulfide, 4,4' -dihydroxydibenzyl sulfide, 4,4',4"-trihydroxytriphenylmethyl ethyl sulfide, bis-(4,4',4"-trihydroxytriphenylmethyl) disulfide, 2,2'-di(p-hydroxyphenyl) ethyl-n-butyl sulfide, 5,6-dihydroxy-2-methyl benzothiazole, 5-hydroxy-1,4-dithianaphthalene, 4-hydroxyphenyl-1'-phenyl-5'-tetrazolyl sulfide, 1-hydroxy-4-(1-phenyl-5-tetrazolylthio) naphthalene, and the like.

(d) Other phenol compounds:

    ______________________________________                                         Phenol Compounds         m.p. (° C.)                                    ______________________________________                                         2-n-butylphenol          125                                                   4-n-butylphenol          120                                                   4-iso-amylphenol         93                                                    4-tert-octylphenol       84                                                    4-n-nonylphenol          40                                                    4-n-dodecylphenol        65                                                    4-n-heptadecylphenol     96                                                    4-n-amylresorcinol       73                                                    4-n-hexylresorcinol      69                                                    4-tert-octylresorcinol   64                                                    3-n-pentadecylcatechol   60                                                    4-n-butoxyphenol         65                                                    4-n-octyloxyphenol       60                                                    n-butyl 4-hydroxybenzoate                                                                               72                                                    n-lauryl 4-hydroxybenzoate                                                     4-n-octylphenyl salicylate                                                                              75                                                    n-hexadecyl 2-hydroxy-2-naphthoate                                                                      73                                                    1-[4-hydroxyphenyl]-pentanone-(3)                                                                       87.5                                                  4-hydroxyphenyl octyl ketone                                                                            98                                                    4-(ω-phenyl-n-octyl)phenol                                                                        81                                                    4-n-octylphenyl phenol   64                                                    4-n-laurylphenyl phenol  82                                                    4-n-laurylphenyl-4-hydroxyphenyl butane                                                                 182                                                   2-benzoyl-5-n-octyloxyphenol                                                                            45                                                    1,10-di(4-hydroxyphenyl)decane                                                                          142                                                   4,4'-(1-methyl-n-heptylidene)diphenol                                                                   88                                                    4,4'-(1-methyl-n-octylidene)diphenol                                                                    56                                                    4,4'-(1-n-butyl-n-pentylidene)diphenol                                                                  170                                                   4,4'-(1-n-pentyl-n-hexylidene)diphenol                                                                  193                                                   3,3'-di-n-butyl-4,4'-isopropylidene diphenol                                                            101                                                   3,3'-di-n-butyl-4,4'-sec-butylidene dephenol                                                            146                                                   3,3'-di-n-butyl-4,4'-bishydroxyphenyl sulfide                                                           129                                                   ______________________________________                                    

In addition, according to the present invention, a color developing accelerating agent such as, for example, weak acids, may be added to the recording layer to prevent color changing and fading of the colored image, enhance the storage stability, and increase the color density.

(IV) Color developing accelerating agents

Representative color developing accelerating agents used in this invention can be classified as shown below.

(i) Phenols, biphenols, diphenol methanes of the following formulas and derivatives thereof: ##STR1## where R₁, R₁ ', R₂, R₂ ', R₃, R₃ ', R₄, R₄ ', R₅, R₅ ', R₆ and R₇ are similar or dissimilar, selected from the class of hydrogen, C₁ -C₃ alkyl, alkoxy, acyl, alkylamino, dialkylamino, amino, nitro, and halogen.

Examples of the above mentioned compounds are: 4-tert-butylphenol, 4-hydroxydiphenoxide, α-naphthol, β-naphthol, methyl 4-hydroxybenzoate, 4-hydroxyacetophenone, 4-tert-octylcatechol, 2,2'-dihydroxydiphenyl, 4-hydroxydiphenyloxide, 2,2'-methylene-bis(4-chlorophenol), 2,2'-methylene-bis(4-methyl-6-tert-butylphenol), 4,4'-isopropylidene diphenol, 4,4'-isopropylidene-bis(2-chlorophenol), 4,4'-isopropylidene bis(2,6-dibromophenol), 4,4'-isopropylidene bis(2-methylphenol), 4,4'-isopropylidene bis(2,6-dimethylphenol), 4,4'-isopropylidene bis(2-tert-butylphenol), 4,4'-sec-butylidene bis(2-methylphenol), 4,4'-cyclohexylidene diphenol, 4,4'-cyclohexylidene bis(2-methylphenol), 2,2'-thiobis(4,6-dichlorophenol), and 4,4'-(1-methyl-n-hexylidene)diphenol.

(ii) Clay minerals

Aluminum oxide, Japanese acid clay, kaolin, silica, etc.

(iii) Organic acids

Aliphatic carboxylic acids, aromatic carboxylic acids, etc.

As the binders, there may be used water-soluble synthetic high polymers, natural high polymers and high polymers of aqueous emulsion type.

Representative binders are polyvinyl alcohol, polyvinyl acrylamide, casein, gelatin, starch and derivatives thereof, cellulose, methyl cellulose, hydroxyethyl cellulose, gum arabic, sodium alginate, zinc sodium sodium zinc caseinate, carboxymethyl cellulose, pectin, copolymer of styrene and maleic anhydride, copolymer of vinyl methyl ether and maleic anhydride, polyacrylates and copolymers of acrylates, polyethylene oxide, styrene-butadiene series emulsions, vinyl chloride series emulsions, and vinyl acetate series emulsions.

The image recording member of the present invention may be prepared, for example, by mixing and uniformly dispersing 2.5-25 parts, preferably 3-15 parts, by weight of the conductive agent, 0.25-5 parts, preferably 0.5-2 parts, by weight of the leuco base, 0.25-15 parts, preferably 0.5-6 parts, by weight of the phenol compounds, and 0.5-10 parts, preferably 0.8-5 parts, by weight of the binder (when a color developing accelerating agent is used, less than 10 parts, preferably less than 5 parts, by weight of the color developing accelerating agent per one part by weight of the phenol compound) and applying the dispersion to a substrate such as paper, resin film, glass plate, metal plate, paper having a metal foil, metal deposited paper, carbon conductive paper.

In the present invention, a specific phenol compound is used as an acidic substance in the color forming system and thereby color changing and fading of the recorded image can be prevented and storage stability remarkably improved.

The image recording member of the present invention may be used for recording such as, for example, receiving signal of facsimile, output of computer, its terminal equipments and data of various kinds of measuring apparatus for industry, medical treatment, and business.

The invention will be understood more readily by reference to the following examples, however, these examples are intended to illustrate the invention and are not to be construed to limit the scope of the invention.

EXAMPLE 1

The examples for illustrating the preparation of phenol compounds according to the present invention are given below.

PREPARATION EXAMPLE 1: PHENOL RESIN-A

    ______________________________________                                         4,4'-isopropylidenediphenol                                                                           68.4     gr.                                            Formaldehyde (a 37% aqueous solution)                                                                 45.0     gr.                                            Concentrated hydrochloric acid                                                                        7.5      ml.                                            Ethanol                90       ml.                                            Water                  67.5     ml.                                            ______________________________________                                    

The above-mentioned ingredients were placed in a flask, mixed and dissolved. The mixture was refluxed with heating on a hot bath for a period of predetermined time and then allowed to cool. The resulting oily material was washed with a mixed solvent of methanol and water (40:60) several times and then it was dissolved in 100 ml of methanol. This solution was poured into 2 liters of water to obtain white powder of a phenolic resin. The phenolic resin was recovered by filtration, dried. The yield was 56-68 gr. The phenolic resin thus prepared is hereinafter called "Phenol resin-A".

PREPARATION EXAMPLE 2: PHENOL RESIN-B

    ______________________________________                                         4,4'-sec-butylidenediphenol                                                                        72.6      gr.                                              Acetaldehyde        24.4      gr.                                              Concentrated hydrochloric acid                                                                     7.5       ml.                                              Ethanol             90        ml.                                              Water               95        ml.                                              ______________________________________                                    

The above-mentioned ingredients were used to repeat the same procedure as that in Preparation Example 1 so that substantially white powder of a phenolic resin was obtained. The phenolic resin thus prepared is hereinafter called "Phenol resin-B".

    ______________________________________                                         Crystal Violet Lactone 1 gr.                                                   Synthetic zeolite (supplied by Union                                            Carbide Co., Molecular Sieve 13X)                                                                    5 gr.                                                   Rutile type titanium oxide                                                                            1 gr.                                                   Water                  13 gr.                                                  ______________________________________                                    

The composition of the above-mentioned ingredients was kneaded in a ball mill for two days and nights to prepare a dispersed liquid of Component-A.

    ______________________________________                                         4,4'-isopropylidenediphenol                                                                           1.5      gr.                                            Phenol resin-A obtained in Preparation                                         Example 1 (the softening temperature                                            of 90° C)      1.0      gr.                                            Synthetic zeolite (supplied by Union                                            Carbide Co., Molecular Sieve 13X                                                                     5.0      gr.                                            Polyvinyl alcohol (the polymerization                                           degree of 1000, the saponification                                             degree of 85%)        2        gr.                                            Water                  20.5     gr.                                            ______________________________________                                    

The composition of the above-mentioned ingredients was kneaded in a ball mill for two days and nights to prepare a dispersed liquid of Component-B.

Both dispersed liquids of Components-A and B were gently mixed and the resulting mixture was coated onto an aluminum deposited paper by using a coating rod and dried to form an electric conduction recording layer thereon so that a recording paper was obtained. The recording paper thus prepared was subjected to recording. In such recording, a stylus was connected to the negative - electrode of a power source and the aluminum deposited layer of the recording paper was connected to the positive + electrode. A voltage of approximately 140 volts was impressed to cause the stylus to scan on the recording paper so that a blue image was obtained. Where the stylus and aluminum layer were connected to the positive and negative electrodes, respectively or when the power source of an alternating current was used, substantially the same image was obtained in each case.

The recordability of the recording paper thus prepared was found excellent in the recordability and, even when it was allowed to stand at 40° C. and 80% RH for two months, both the physical property of its surface and recordability remained very good. Further, even when the recording paper having been subjected to recording was allowed to stand under the same condition, its quality did not change at all at the image region and the non-image region and the physical property of the surface remained excellent and further no change of the color was recognized.

In the foregoing, there has been shown the example using the Phenol resin-A having a softening point of 90° C. Meanwhile, various Phenol resins-A prepared under the various different polymerization conditions were separately used to prepare recording papers in the same manner as above.

The general evaluation of the recording papers thus prepared was made with respect to the change of the color of the formed image with the lapse of time, the surface physical property and recordability of the recording papers allowed to stand at 40° C. and 80% RH for one month. When the recording paper having been subjected to recording was allowed to stand under the same conditions as above, the color change of the formed image with the lapse of time was observed. With respect to the surface physical property and the recordability, they were evaluated by comparing with those of the recording paper immediately after being prepared.

The results of the general evaluation are shown in Table 1.

                  Table 1                                                          ______________________________________                                                         Time for poly-                                                                             Softening                                          Recording                                                                              Phenol  merizing Phenol                                                                            temperature                                                                             General                                   paper   resin-A resin-A (hour)                                                                             (° C.)                                                                           evaluation                                ______________________________________                                         1       A-1     0.5          52      ⊚                          2       A-2     1.0          65      ⊚                          3       A-3     1.5          90      ⊚                          4       A-4     2.0         111      ⊚                          5       A-5     2.5         130      ⊚                          6       A-6     3.0         155      ○                                  7       A-7     5.0         180      Δ                                   8       A-8     7.0         --       X                                         ______________________________________                                         Recording paper                                                                            Allowed to stand at 40° C and                                                              Δ                                         containing no phenol                                                                       80% RH for 3 days                                                  resin       Allowed to stand at 40° C and                                                              X                                                           80% RH for two weeks                                               ______________________________________                                          ⊚ No change observed in the image color with lapse of time      the surface physical property and the recordability.                           ○ Slight change observed in the same points.                            Δ Considerable change observed.                                          X Extreme change observed.                                               

EXAMPLE 2

Other examples for preparing phenol compounds according to the present invention are given below.

PREPARATION EXAMPLE 3: IPCS RESIN

    ______________________________________                                         4,4'-isopropylidenedicatechol                                                                       52.0       gr.                                            Sulfur dichloride    31.5       gr.                                            Chloroform           1800       ml.                                            Acetone              50         ml.                                            ______________________________________                                    

The above-mentioned ingredients were placed in a flask, mixed, dissolved and reacted with stirring at 50° C. for a period of predetermined time and then allowed to cool. The whole solution was evaporated to dryness one time and the product was washed several times with a mixed solvent of water and alcohol (70:30), dissolved in 100 ml. of methanol and reprecipitated in 2 liters of water to obtain a phenolic resin of white powder tinged slightly with brown. The phenolic resin was recovered by filtration and dried. The yield was 51 gr. The resulting resin is hereinafter called "IPCS resin".

PREPARATION EXAMPLE 4: BHSS RESIN

    ______________________________________                                         4,4'-bishydroxyphenylsulfide                                                                       21.8      gr.                                              Sulfur              9.6       gr.                                              Sodium hydroxide    4.0       gr.                                              1,2,4-trichlorobenzene                                                                             300       ml.                                              ______________________________________                                    

The above-mentioned ingredients were mixed and reacted with stirring at 190° C. for 4 hours. After cooling, an excess of the sulfur was removed and the reaction mixture was neutralized with a 30% aqueous solution of acetic acid. The resulting oil layer was distilled under reduced pressure to remove the solvent. Subsequently, the same treatment as in Preparation Example 1 was repeated to obtain a phenol resin of light brown powder. The phenol resin thus obtained is hereinafter called "BHSS resin".

In the meantime, 5 gr. of 1,3,3-tri-methylindolino-8'-methoxybenzopyrylspiran, 1 gr. of rutile type titanium oxide, 3 gr. of polyvinyl alcohol (the polymerization degree of 1000, the saponification degree of 85%) and 12 gr. of water were kneaded in a ball mill for two days and nights to prepare a dispersed light of Component-A.

Further, 8 gr. of IPCS resin (the softening temperature of 118° C.), 1 gr. of rutile type titanium oxide, 3 gr. of polyvinyl alcohol (the polymerization degree of 1000, the saponification degree of 85%) and 12 gr. of water were kneaded for two days and nights to prepare a dispersed liquid of Component-B.

Both dispersed liquids of components-A and B were dispersed along with 1 gr. of aluminum powder and the resulting dispersed mixture was coated onto an aluminum deposited paper in the same manner as in Example 1 to prepare a recording paper. An electrode for a return circuit was taken from the surface of the recording paper thus prepared by means of an aluminum plate and a DC voltage of approximately 100 volts was impressed between the electrode for a return circuit and a stylus (positive electrode) to cause the stylus to scan so that a reddish purple image was obtained. The stability of the image with the lapse of time was found to be excellent and, as the result of the preservation test at 40° C. and 80% RH for one month, no decrease in the image density could be observed.

EXAMPLE 3

In a ball mill, 3 gr. of lactam of 9-p-nitroanilino-3,6-bis(diethylamino)-9-xanthenyl-o-benzoic acid, 1 gr. of rutile type titanium oxide, 9 gr. of poly-4-vinylbenzyltrimethyl ammonium chloride (ECR-34, trade name for a product of Dow Chemical Co., a 30% aqueous solution) and 7 gr. of water were kneaded for two days and nights to prepare a dispersed liquid of Component-A.

On the other hand, 8 gr. of BHSS resin (the softening temperature of 144° C.) obtained in Preparation Example 4, 1 gr. of rutile type titanium oxide, 9 gr. of poly-4-vinylbenzyltrimethyl ammonium chloride (ECR-34, a trade name for a product of Dow Chemical Co., a 30% aqueous solution) and 7 gr. of water were kneaded in a ball mill for two days and nights to prepare a dispersed liquid of Component-B.

An electric conduction recording layer was formed on an aluminum deposited paper in the same manner as in Example 1 to prepare a recording paper. A stylus was connected to the negative electrode of the power source and the aluminum layer was connected to the positive electrode to cause the stylus to scan by applying a voltage of 140 volts so that a reddish purple image was obtained. The result of the preservation test conducted in the same manner as in Example 1 was found extremely excellent.

EXAMPLE 4

The recordability of various recording papers prepared by using various kinds of electrically conductive agents were tested as shown below.

The same procedure as in Example 1 was repeated except that the electrically conductive agents listed in Table 2 below were separately used in place of the synthetic zeolite to prepare recording papers. The recordability of the recording papers was evaluated to obtain the results as shown in Table 2.

                  Table 2                                                          ______________________________________                                         Electrically      Recording                                                    conductive                                                                              Amount   voltage   Polarity                                           agent    (gr.)    (volt)    of stylus                                                                             Recordability                               ______________________________________                                         Al       1.0      110       (+)    ⊚                            ZnO      5.0      180       (+)    ⊚                            SnO.sub.2                                                                               4.0      130       (+)    ⊚                            ZnS      5.0      150       (-)    ○                                    Cu.sub.2 I.sub.2                                                                        4.0      130       (+)    ⊚                            AlP      3.0      150       (-)    ○                                    SiC      4.0      160       A C    ○                                    MgTe     1.0      110       A C    ○                                    ______________________________________                                          ⊚ . . . very good                                               ○ . . . good                                                      

In addition, a material selected from zeolite minerals and zeolite-analogous minerals listed in Table 3 below was used in place of Molecular Sieve 13X used in Example 1 to prepare a recording paper in the same manner as in Example 1. The recording paper was evaluated in accordance with the evaluating method described in Example 1 to obtain the results as shown in Table 3.

                  Table 3                                                          ______________________________________                                         Zeolite mineral and zeolite                                                                          General                                                  analogous mineral     evaluation                                               ______________________________________                                         Faujasite             ⊚                                         Erionite              ○                                                 Analcite              Δ                                                  Molecular Sieve SK-40*.sup.1                                                                         ⊚                                         Zeolon.sup.*2         ○                                                 Natrolite             ○                                                 Garronite             Δ                                                  Clinoptilotite        Δ                                                  Molecular Sieve 5A.sup.*3                                                                            ○                                                 Gonnardite            ○                                                 ______________________________________                                          .sup.*1,3 trade names for the synthetic zeolite of Union Carbide Co.           .sup.*2  trade name for the synthetic zeolite of Norton Co.              

EXAMPLE 5

In a ball mill, 5 gr. of Rhodamine B lactone, 25 gr. of zinc oxide rendered electrically conductive and 70 gr. of water were kneaded for two days and nights to prepare a dispersed liquid of Component-A.

On the other hand, 13 gr. of 2,2'-dihydroxy-5,5'-dichlorodiphenylsulfide, 20 gr. of zinc oxide rendered electrically conductive, 10 gr. of polyvinyl alcohol (the polymerization degree of 1000, the saponification degree of 85%) and 70 gr. of water were kneaded in a ball mill for two days and nights to prepare a dispersed liquid of Component-B.

These dispersed liquids of Components-A and B were treated in the same manner as in Example 1 to coat the resulting mixture onto an aluminum deposited paper so that a recording paper was prepared. Electric current was caused to flow in such a manner that a stylus was connected to the negative electrode, the aluminum layer was connected to the positive electrode and a voltage of approximately 120 volts was applied. As the result, a red good image was obtained.

In addition, the recording paper bearing the image was exposed to a white fluorescent light source at 5000 lux for 200 hours to carry the test with respect to the light resistance property. As a result of such test, the decrease in the density of the image was only about 15% and the ground color of the recording paper hardly turned yellow, and therefore, the light resistance property was found to be excellent.

EXAMPLE 6

The same procedure as that in Example 5 was repeated except that phenol compounds listed in Table 4 were separately used in place of 2,2'-dihydroxy-5,5'-dichlorodiphenylsulfide to prepare recording papers. The prepared recording papers were subjected to electric conduction recording and the light resistance property thereof was tested. The recording and exposure conditions were the same as those in Example 5.

                  Table 4                                                          ______________________________________                                                          Image density                                                                           Change of                                            No.    Phenol compound (*1)    (*2) ground color                               ______________________________________                                         1      4,4'-dihydroxydiphenyl-                                                                        0.78    0.66 No change                                         sulfide                                                                 2      4,4'-dihydroxydiphenyl-                                                                        0.76    0.64 No change                                         disulfide                                                               3      4,4'-dihydroxydiphenyl-                                                                        0.81    0.65 Slightly                                          sulfone                      turned yellow                              4      4,4'-dihydroxydiphenyl-                                                                        0.79    0.65 No change                                         sulfoxide                                                               5      4-hydroxyphenyl-2'-                                                                            0.77    0.71 No change                                         chlorobenzylsulfide                                                     6      4,4'-dihydroxythioben-                                                                         0.77    0.62 Slightly                                          zophenone                    turned yellow                              7      2,2',4,4'-tetrahydroxy-                                                                        0.82    0.69 No change                                         diphenyldisulfide                                                       8      4,4'-di(p-hydroxyphenyl)                                                                       0.78    0.70 No change                                         diphenylsulfide                                                         9      5-hydroxy-1,4-dithio-                                                                          0.79    0.66 Slightly                                          naphthalene                  turned light                                                                   brown                                      10     2,2'-dihydroxy-6,6'-                                                                           0.80    0.69 No change                                         dinaphthyldisulfide                                                     Compari-                                                                              4,4'-isopropylidene-                                                                           0.78    0.41 Turned yellow                              son    diphenol                                                                material                                                                              4,4'-cyclohexylidene-                                                                          0.77    0.43 Turned yellow                                     diphenol                                                                ______________________________________                                          *1 Measured immediately after recording.                                       *2 Measured after the image was exposed to a white fluorescent light           source at 5000 lux for 200 hours.                                        

EXAMPLE 7

In a ball mill, 3 gr. of lactam of 9-p-nitroanilino-3,6-bis-(diethylamino)-9-xanthenyl-o-benzoic acid, 1 gr. of rutile type titanium oxide, 9 gr. of poly-4-vinylbenzyltrimethyl ammonium chloride (ECR-34, a trade name for a product of Dow Chemical Co., a 30% aqueous solution) and 7 gr. of water were kneaded for two days and nights to prepare a dispersed liquid of Component-A.

Further, 8 gr. of 4,4'-di-n-butyl 2,2'-thio-bis (6-chlorophenol), 1 gr. of rutile type titanium oxide, 9 gr. of poly-4-vinylbenzyltrimethyl ammonium chloride (ECR-34, a trade name for a product of Dow Chemical Co., a 30% aqueous solution) and 7 gr. of water were kneaded in a ball mill for two days and nights to prepare a dispersed liquid of Component-B.

These dispersed liquids of Components-A and B were used to form an electric conduction recording layer on an aluminum deposited paper in the same manner as in Example 1 so that a recording paper was prepared. A stylus was connected to the negative electrode and the aluminum deposited layer was connected to the positive electrode to cause the stylus to scan on the recording paper by impressing a voltage of 140 volts so that a reddish purple image was obtained.

As the result of the preservation test conducted in the same manner as in Example 1, no deterioration of the property of the recording paper could be observed and the property was found very excellent.

In addition, when the compounds as mentioned below were used in place of the phenol compound, the same effect as above was observed.

2-benzoyl-5-n-octyloxyphenol,

4-n-octylphenylphenol,

4,4'-(1-methyl-n-heptylidene)diphenol,

4,4'-(1-methyl-n-hexylidene)diphenol,

4-n-butyl phenol,

4,4'-(1-n-pentyl-n-hexylidene)diphenol, and

4,4'-(1-n-butyl-n-pentylidene)diphenol

EXAMPLE 8

The effect due to the simultaneous use of a weak acid as a color developing accelerating agent was particularly tested as described below.

In the procedure for preparing a recording paper of Example 1, 4,4'-sec-butylidenediphenol was substituted for 4,4'-isopropylidenediphenol and the amount of each of 4,4'-sec-butylidenediphenol and Phenol resin A was varied as shown in Table 5 to prepare recording papers in the same manner. The recording papers thus prepared were separately subjected to electric conduction recording in the following manner. The aluminum deposited layer was connected to the positive electrode and a tungsten stylus of 0.2 mm in diameter was connected to the negative electrode to cause the stylus to scan on the recording paper at a linear density of 4 line/mm and a linear velocity of 70 cm/sec by impressing a voltage of approximately 150 volts.

The density of the image immediately after recording and the density of the image preserved at 40° C. and 80% RH for one month after recording are shown in Table 5. The image density was measured by using a macbeth type densitometer with a green filter.

                  Table 5                                                          ______________________________________                                               Amount of 4,4'-                                                                              Amount of                                                  Sample                                                                               butylidenediphenol                                                                           Phenol resin-A                                                                             Image Density                                  No.   (gr.)         (gr.)       (1).sup.*1                                                                           (2).sup.*2                               ______________________________________                                         1     0             2.5         0.80  0.80                                     2     0.5           2.0         0.85  0.75                                     3     1.0           1.5         0.91  0.68                                     4     1.5           1.0         0.95  0.62                                     5     2.0           0.5         0.98  0.55                                     6     2.5           0           1.10  0.21                                     ______________________________________                                          .sup.*1 Image density measured immediately after recording.                    .sup.*2 Image density measured after the image was preserved at 40.degree      C. and 80% RH for one month.                                              

We claim:
 1. In an electrical recording member which comprises a substrate and a recording layer overlying said substrate and containing, dispersed in a binder, a conductive agent, a leuco base and an acidic substance, whereby said leuco base and acidic substance react to produce an image upon the passage of an electric current through said recording layer, the improvement wherein said acidic substance consists essentially of a phenolic resin having a softening point of from 40° to 200° C. and obtained by the polycondensation of 4,4'-isopropylidene diphenol or 4,4'-sec-butylidene diphenol with formaldehyde or acetaldehyde.
 2. An image recording member according to claim 1 in which the recording layer further contains a weak acid as a color developing accelerating agent.
 3. An image recording member according to claim 1 in which the conductive agent is metallic powder.
 4. An image recording member according to claim 1 in which the conductive agent is at least one member selected from the group consisting of metal oxides, metal sulfides, metal phosphides, and metal halides.
 5. An image recording member according to claim 1 in which the conductive agent is at least one member selected from the group consisting of zeolite minerals and zeolite-like minerals.
 6. An image recording member according to claim 1 in which the conductive agent is a conductive polymer.
 7. An image recording member according to claim 1 in which the leuco base is selected from the group consisting of triphenylmethane series, fluoran series, phenothiazine series, auramine series and spiropyran series dye leuco bodies.
 8. An image recording member according to claim 1 in which the weight ratio of conductive agent: leuco base: phenolic resin: binder in the recording layer is 2.5- 25:0.25- 5:0.25- 15:0.5-
 10. 9. An image recording member according to claim 1 in which the weight ratio of conductive agent: leuco base: phenolic resin: binder in the recording layer is 3- 15:0.5- 2:0.5- 6:0.8-
 5. 10. An image recording member according to claim 1 in which the substrate is conductive.
 11. An image recording member according to claim 2 in which the weak acid is at least one member selected from the group consisting of phenols, biphenols, diphenol methanes of the following formulas and derivatives thereof: ##STR2## where R₁,R'₁,R₂,R'₂,R₃,R'₃,R₄,R'₄,R.sub.5,R'₅,R₆ and R₇ are similar or dissimilar and are selected from the group consisting of hydrogen, C₁ -C₃ alkyl, alkoxy, acyl, alkylamino, dialkylamino, amino, nitro, and halogen.
 12. An image recording member according to claim 2 in which the weak acid is at least one member selected from the group consisting of 4-tert-butylphenol, 4-hydroxydiphenoxide, α-naphthol, β-naphthol, methyl 4-hydroxybenzoate, 4-hydroxyacetophenone, 4-tert-octylcatechol, 2,2'-dihydroxydiphenyl, 4-hydroxydiphenyloxide, 2,2'-methylene-bis(4-chlorophenol), 2,2'-methylene-bis(4-methyl-6-tert-butylphenol), 4,4'-isopropylidene diphenol, 4,4'-isopropylidene-bis(2-chlorophenol), 4,4'-isopropylidene-bis(2,6-dibromophenol), 4,4'-isopropylidene bis(2-methylphenol), 4,4'-isopropylidene bis(2,6-dimethylphenol), 4,4'-isopropylidene bis(2-tert-butylphenol), 4,4'-sec-butylidene bis(2-methylphenol), 4,4'-cyclohexylidene diphenol, 4,4'-cyclohexylidene bis(2-methylphenol), 2,2'-thiobis(4,6-dichlorophenol), and 4,4'-(1-methyl-n-hexylidene)diphenol.
 13. An image recording member according to claim 2 in which the weak acid is a clay mineral.
 14. An image recording member according to claim 2 in which the weak acid is an aliphatic carboxylic acid or an aromatic carboxylic acid.
 15. An image recording member according to claim 2 in which the weak acid is contained in the recording layer in an amount of less than 10 parts by weight per one part by weight of the phenolic resin.
 16. An image recording member according to claim 2 in which the weak acid is contained in the recording layer in an amount of less than 5 parts by weight per one part by weight of the phenolic resin.
 17. An image recording member according to claim 1 in which the recording layer is a single layer containing said conductive agent, said leuco base, said phenolic resin, and said binder.
 18. An image recording member according to claim 1 in which the recording layer is composed of a conduction layer containing mainly said conductive agent and an image forming layer containing mainly said leuco base and said phenolic resin.
 19. In a process for conduction recording comprisingcontacting a stylus with a recording layer provided on a substrate having a conductive layer, said recording layer containing, dispersed in a binder, a conductive agent, a leuco base and an acidic substance; setting a return electrode on said conductive layer; and applying an electric current to said recording layer through said stylus to cause said leuco base and said acidic substance to react and thereby form an image; the improvement wherein said acidic substance consists essentially of a phenolic resin having a softening point of from 40° to 200° and obtained by the polycondensation of 4,4'-isopropylidene diphenol or 4,4'-sec-butylidene diphenol with formaldehyde or acetaldehyde.
 20. In a process for conduction recording comprisingcontacting a stylus with a recording layer provided on a substrate, said recording layer containing, dispersed in a binder, a conductive agent, a leuco base and an acidic substance; setting a return electrode on said recording layer; and applying an electrode current to said recording layer through said stylus to cause said leuco base and said acidic substance to react and thereby form an image; the improvement wherein said acidic substance consists essentially of a phenolic resin having a softening point of from 40° to 200° C. and obtained by the polycondensation of 4,4'-isopropylidene diphenol or 4,4'-sec-butylidene diphenol with formaldehyde or acetaldehyde.
 21. An image recording member according to claim 4, wherein said metal oxide is an oxide of a metal selected from the group consisting of titanium, zinc, lead, tin, calcium, nickel, indium, tin-indium, molybdenum, and tungsten; wherein said metal sulfide is selected from the group consisting of zinc sulfide, calcium sulfide, copper sulfide, Cd₄ GeS₆, Cd₄ SiS₆, Zn₄ GeS₆ and Zn₄ SiS₆ ; wherein said metal phosphide is a member selected from the group consisting of aluminum phosphide, gallium phosphide and gallium aluminum phosphide; and wherein said metal halide is a member selected from the group consisting of copper chloride, silver chloride, silver bromide, silver iodide, thallium chloride, thallium iodide, lead chloride and cuprous iodide.
 22. An image recording member according to claim 6, wherein said conductive polymer is poly-4-vinylbenzyltrimethylammonium chloride or sodium polymethylacrylate.
 23. An image recording member according to claim 13, wherein said clay mineral is a member selected from the group consisting of aluminum oxide, Japanese acid clay, kaolin and silica.
 24. An image recording member according to claim 1 wherein said binder is a member selected from the group consisting of polyvinyl alcohol, polyvinyl acrylamide, casein, gelatin, starch, starch derivatives, cellulose, methyl cellulose, hydroxyethyl cellulose, gum arabic, sodium alginate, zinc sodium caseinate, sodium zinc caseinate, carboxymethyl cellulose, pectin, copolymers of styrene and maleic anhydride, copolymers of vinyl methyl ether and maleic anhydride, polyacrylates, acrylate copolymers, polyethylene oxide, styrene-butadiene series emulsions, vinylchloride series emulsions and vinylacetate series emulsions. 